Semiconductor storage devices such as a NAND flash memory have been downscaled to increase storage capacity. Development of memories using new materials is progressing to achieve further downscaling. Novel memories such as a resistance random access memory (ReRAM), a phase-change RAM (PRAM), a phase-change memory (PCM), an interfacial PCM (iPCM), a ferroelectric NAND-type memory (FeNAND), and a magnetic random access memory (MRAM) are developed.
Among these novel memories, the PCM and the iPCM are brought to a low resistance state (a set state) or a high resistance state (a reset state) according to phase transition of a phase-change film of the relevant memory cell. This enables the PCM and the iPCM to store therein logical data.
In the PCM, an operation called “slow cooling” of slowly sinking a voltage applied to the memory cell is required to rewrite a Reset state with a Set state. This is because it is considered that, if a voltage applied to the memory cell is rapidly sunk, it is possible that the memory cell is not changed from the Reset state to the Set state or returns to the Reset state. It is also considered that the slow cooling operation may be required in the iPCM not only when the Reset state is to be rewritten with the Set state but also when the Set state is to be written with the Reset state.
Therefore, the PCM and the iPCM require a configuration that enables to adjust a rate at which a voltage of a bit line is sunk.